This invention relates to a copying process wherein electrostatic latent images are formed on surface layer of photosensitive material or dielectric material, developed, transferred and then fixed to form the final images and, in particular to magnetic brush developing and cleaning process wherein the development and cleaning are performed by a single magnetic brush.
2. Description of the Prior Art
It has been known to form electrostatic latent images on the surface layer of photosensitive or dielectric material, to develop such electrostatic latent images by magnetic brush developing process, to transfer the resulting toner images on a transferring sheet of conventional paper or the like, to fix the transferred images by a pressure and/or heating to provide a hard copy, and then to remove the toner remained on the surface of an image holding member and to repeat again the cycle as outlined hereinabove.
Known magnetic brush developing systems for carrying out such a copying process include those disclosed by Anckerson et. al. (U.S. Pat. No. 3,455,276), Nishihama et. al. (U.S. Pat. No. 4,081,571), Asanae et. al. (U.S. Pat. No. 4,231,320), etc.
In such a copying process, one copying cycle is completed ordinarily by one revolution of an image-bearing member which comprises an endless belt or drum. It has been proposed to clean toner remaining on the belt or drum after the transference by means of the magnetic brush employed for the development and such a system has been put into practical use in several copying apparatus. In such a system, electrostatic latent images are formed and developed during one revolution of electrostatic latent image-bearing member and the developed image is transferred, electric change is removed and the remaining toner is cleaned by means of the same magnetic brush during another revolution. Namely, one copying cycle has been completed during two revolutions of the image bearing member. As a cleaning apparatus is not required separately, such a system has advantages in that there can be provided a compact, light weight and inexpensive copying apparatus having a simple structure. However, it is very unreasonable to effect the development and cleaning by a single magnetic brush for the case using one component magnetic toner as compared with the case using two component developer. In addition, known magnetic toners include those disclosed by Nelson et. al. (U.S. Pat. No. 3,639,245), Noguchi et. al. (U.S. Pat. No. 4,189,390), Kawanishi et. al. (U.S. Pat. No. 4,265,993), etc.
Although it has been proposed by Narita (U.S. Pat. No. 3,918,808) to employ jointly a blade during the cleaning process and it has been visualized to employ jointly a fur brush, such means have disadvantages in that the copying apparatus becomes large or that the surface of the image bearing member tends to be damaged. It has been also proposed in Japanese Laid Open Utility Model No. 55-95150 to reduce the contacting width of magnetic toner in contact with the photosensitive material during the developing process by employing an adjusting member. It has been further proposed in Japanese Laid Open Patent No. 55-6303 to alternate the relative condition of magnetic brush to the shell during the developing process and cleaning process by alternating the position of developing magnet poles. The use of such arrangements complicates the mechanism and reduces the reliability of the copying apparatus in each case.